High speed electronic control of fluid flow using inexpensive batch fabricated valve arrays is potentially critical for numerous applications, including distributed actuator controls, paper or object positioning, dynamic control of fluid instabilities, or microcontrol of microchemical reactions and biological assays. Other potential applications include use of valves to drive physical elements that support tactile displays or other virtual reality interface tools. However, large two dimensional arrays of microvalves (e.g. 100.times.100 valves or more) can be difficult and expensive to construct to the necessary tolerances, and reliable addressing of specific valves to open or close on a millisecond time scale is often not feasible.
The present invention provides a novel bistable valve capable of being arranged in two dimensional valve arrays, with each valve in the array being controlled by passive matrix addressing. In a preferred embodiment, each valve includes a valve housing having an aperture plate defining an aperture therethrough, and an opposing plate positioned in spaced apart relationship to the aperture plate. A flexible electrically conductive film or strip is attached at its first end to the aperture plate and at its second end to the opposing plate. Valve action is provided by use of at least two switching electrodes for moving the flexible film between an aperture blocking position and an aperture open position, with at least one of the switching electrodes positioned adjacent to the aperture plate and at least one of the switching electrodes positioned adjacent to the opposing plate. To reduce unswitched movement when the switching electrode bias is reduced or not present, at least two catches are used. Generally, one of the catches is positioned adjacent to the aperture plate and at least one of the catches positioned adjacent to the opposing plate. These catches hold the film or strip in either a generally S-shaped aperture blocking or non-blocking position when switching forces are absent, but are insufficiently strong to prevent switching when the switching electrodes are activated.
The catches can be either mechanical, electrical, or even electromechanical. For example, an electrical catch can be provided by two catch electrodes, held at a constant catch voltage bias. If the catch voltage bias is substantially less than the switch voltage bias applied to the switching electrodes when moving the flexible film, the catches do not substantially interfere with switch action, yet still help maintain the flexible film in a constant position even when the switch voltage is no longer present. Advantageously, the provision of electrical catches minimizes migration or movement of the S-shaped flexure along the film in response to fluid forces. Similarly, mechanical catches that rely on lip structures, detents, or other suitable devices, alone or in combination with electrical catches, can result in an applied stress bias that holds the film in position with a small catch force. Again, this catch force is usually substantially less than the switching force applied when switching the film between a blocking and non-blocking position.
In preferred embodiments, various valve modifications can be employed to enhance valve operation, minimize power requirements, and increase valve switching times. For example, instead of a circular or elliptical aperture cross section, the aperture can be defined to have at least one acute vertex, providing a point release for air inflow or outflow. The flexible film does not have to be a straight, homogenous strip, but can be varied in composition, width, thickness, and stiffness along its length. For example, the flexible film can have a first narrow neck attachable to the aperture plate, a second narrow neck attachable to the opposing plate, and a wide body therebetween capable of assuming a generally S-shaped configuration. In other configurations, the flexible film can have a generally U-shaped configuration, with a first end attachable to the aperture plate and a second end attachable to the opposing plate. In still other configurations, electrode size, positioning, and geometry can be varied. For example, narrow electrodes can be provided adjacent to the narrow necks of the film, while electrodes can be widened where they are adjacent to the body of the film. These electrode modifications, and other mechanical modifications to the flexible film, allow for tuning valve response time, decreasing or increasing valve pressure strengths, and varying electrostatic interactions.
Advantageously, valves of the present invention can be arranged into large passively addressable arrays. Such arrays include a plurality of valves, with each valve defining an aperture therethrough, and a plurality of flexible films respectively attached to each of the plurality of valves, with each flexible film independently addressable to alternately switch between an aperture blocking position and an aperture open position. A switching voltage source is used to maintain a subset of the plurality of valves at either a non-switching voltage or a switching voltage. When switching electrodes are activated for applying an electrostatic switching force to move the plurality of flexible films, only that subset of the plurality of valves having flexible films maintained at the switch voltage switch between the aperture blocking position and an aperture open position. In practice, usually three address lines (with each address line having two possible voltages) connected to each valve in a valve array are required. Opposing switching electrodes are respectively addressed at one of two possible voltage (e.g. 100 volts and 0 volts, or 50 volts and -50 volts). To switch the film from a blocking to a non-blocking position, or vice versa, it is necessary to switch the voltages. When a particular valve in a two dimensional row and column array is to be switched, the voltage applied to all flexible strips in a particular row (or column) is changed from an intermediate voltage (e.g. 50 volts or 0 volts) to a switching voltage. Ordinarily, only that valve at the intersection of the row (or column) and column (or row) of opposing electrodes actually switches, with the others valves addressed in the array remaining unchanged. Of course, by appropriate row and column addressing, multiple switching in parallel is possible.
In a preferred embodiment, the use of independently addressable valves allows for high spatial precision transport of objects, including flexible objects such as paper. For certain applications, including processing of high purity or delicate materials, contamination or damage to the object may result from mechanical grasping or contact. This is particularly true for high speed processing systems, which may damage objects simply by engaging them. For example, high speed rollers may damage paper through differential engagement of misaligned paper with the roller, resulting in ripping or tearing of the paper. Fortunately, mechanical or frictional engagement is only one possible means for moving an object. Object drive mechanisms based on various fluid support techniques have long been employed to move delicate objects without requiring solid mechanical contact. For example, instead of using conventional belts, conveyors or rollers, paper moving through xerographic copier systems can be supported on a laminar air flow, or uplifted and moved by valve controlled air jets. This is particularly advantageous, for example, when sheets of paper carrying unfixed toner images must be moved between a photoconductive drum and a fusing station where the toner image is fixed. With conventional physical rollers, the continuing possibility of dynamic distortions to the toner image, or even slight misalignments resulting in image degradation, must always be considered.
Accordingly, the present invention provides a fluid transport apparatus and method for moving a flexible object that does not require physical contact. The present invention can effectively work with either continuous or discrete flexible objects moving through a materials processing system. A fluid pressure source is connected to a plurality of valves, with each valve defining an aperture therethrough, and having a plurality of flexible films respectively attached, with each flexible film independently addressable to alternately switch between an aperture blocking position and an aperture open position. A switching voltage source maintains a subset of the plurality of valves at one of a non-addressed voltage and an address voltage, and a plurality of switching electrodes apply an electrostatic switching force to move the plurality of flexible films, with only that subset of the plurality of valves having flexible films maintained at the address voltage switching between the aperture blocking position and an aperture open position.
Additional functions, objects, advantages, and features of the present invention will become apparent from consideration of the following description and drawings of preferred embodiments.